1. Field of the Invention
The present invention relates to a control apparatus for changing the operating characteristic of an internal combustion engine in accordance with the operating state thereof, and more particularly, it relates to a control apparatus for an internal combustion engine which servers to control, for example, the opening and closing timing (valve timing) of an intake valve and an exhaust valve by changing the phase angle of a camshaft with respect to that of a crankshaft of the internal combustion engine.
2. Description of the Related Art
Conventionally, there has been known a control apparatus for an internal combustion engine which can change the operating characteristic of the internal combustion engine by means of an actuator.
Hereinafter, reference will be made, as an example, to a case where the operating characteristic of an internal combustion engine is the phase angle of a camshaft with respect to that of a crankshaft of the internal combustion engine.
A known valve timing control apparatus for an internal combustion engine includes an intake valve and an exhaust valve that are driven to operate in synchronization with the rotation of the internal combustion engine so as to open and close an intake passage and an exhaust passage, respectively, leading to a combustion chamber of the internal combustion engine, a valve timing variable mechanism that changes the opening and closing timing of the intake valve or the exhaust valve by changing the phase angle of a camshaft with respect to a crankshaft of the internal combustion engine, an operating state detection section that detects the operating state of the internal combustion engine (hereinafter also referred to as an engine operating state), a target operating characteristic calculation section (target valve timing calculation section) that calculates a target phase angle of the camshaft (target valve timing and target operating characteristic) in accordance with the engine operating state, an actual operating characteristic detection section (actual valve timing detection section) that detects an actual phase angle of the camshaft (actual valve timing and actual engine operating characteristic), and an operation amount feedback control section (actual valve timing control section) that calculates an amount of operation (a quantity of control) for the valve timing variable mechanism according to feedback control (hereinafter also referred to as “F/B control”) so as to make the target phase angle and the actual phase angle coincide with each other (see, for example, a first patent document: Japanese patent application laid-open No. 2001-152886).
In this valve timing control apparatus, the actual operating characteristic detection section detects the actual phase angle of the camshaft at every predetermined crank angle. In addition, the operation amount feedback control section calculates the amount of operation for the valve timing variable mechanism based on the detected actual phase angle according to phase angle feedback control at a fixed period (e.g., 25 msec) different from the detection period of the actual phase angle.
Accordingly, the actual phase angle is detected, and the amount of operation for the valve timing variable mechanism is calculated based on the actual phase angle, so that the valve timing variable mechanism is driven to operate based on the amount of operation thus calculated.
As a result, there is a possibility that a control delay time until the start of operation of the valve timing variable mechanism might be lengthened.
Hereinafter, reference will be made to the control delay time due to the above-mentioned known valve timing control apparatus while referring to a timing chart in FIG. 12.
FIG. 12 is the timing chart that shows the control delay time occurring when the operation amount feedback control section executes the phase angle feedback control at a fixed period Tfb in the known valve timing control apparatus.
Here, description will be made to a case where the actual phase angle is detected immediately after the execution of the phase angle feedback control.
In FIG. 12, a control delay time Tcntd is the sum total of an actual phase angle detection delay time Tpdd occurring upon detection of the actual phase angle, a phase angle feedback control processing delay time Tfbd occurring upon execution of the phase angle feedback control, and a PWM driving delay time Tpwmd occurring upon driving the valve timing variable mechanism in a PWM (Pulse Width Modulation) manner.
Here, note that the actual phase angle detection delay time Tpdd is set, as a general delay time, to ½ of a period Tsgt of the crank angle signal for example.
At this time, the actual phase angle is detected immediately after the execution of the phase angle feedback control, so the phase angle feedback control processing delay time Tfbd becomes equal to one fixed period Tfb of the phase angle feedback control.
That is, owing to a deviation between the detection timing of the actual phase angle and the execution timing of the phase angle feedback control, the control delay time Tcntd will contain the phase angle feedback control processing delay time Tfbd corresponding, at maximum, to the one fixed period Tfb of the phase angle feedback control, so the control delay time Tcntd becomes longer.
Accordingly, when the gain of the phase angle feedback control is set to a large value so as to improve the response of the actual phase angle, the actual phase angle causes hunting due to the above-mentioned control delay time Tcntd.
Thus, the gain of the phase angle feedback control can not be set to a large value, so the response time of the actual phase angle is lengthened.
In addition, in this valve timing control apparatus, when the internal combustion engine is rotating at a low speed of about 600 rpm for instance, the detection period of the actual phase angle (e.g., 50 msec when the actual phase angle is detected at every crank angle of 180 degrees) becomes longer than the fixed period (25 msec) of the phase angle feedback control.
Accordingly, the amount of operation for the valve timing variable mechanism is repeatedly calculated based on the same actual phase angle that is different from the actual phase angle until the actual phase angle is detected and updated.
In the known valve timing control apparatus for an internal combustion engine, the gain of the phase angle feedback control can not be set to a large value, so there has been a problem that the response time of the actual phase angle becomes relatively long.
In addition, when the internal combustion engine is rotating at low rotational speed, the amount of operation for the valve timing variable mechanism is repeatedly calculated based on the same actual phase angle that was previously detected and is different from a current actual phase angle until the current or fresh actual phase angle is detected and updated, so there has also been a problem that the control accuracy of the actual phase angle is reduced.